Ultrasound imaging provides information about the interior of a subject. For example, ultrasound imaging can be used to generate an image of a blood vessel and estimate blood flow velocity inside the blood vessel.
With conventional blood flow velocity estimation, a pulse-echo field oscillates in the axial direction along the axis of the ultrasound beam. This is illustrated in FIG. 1 in which a transducer array 100 produces an ultrasound beam 102 that propagates in the axial direction along the z-axis (or depth) 104. Blood scatterers passing through the field of interest produce a signal with a frequency component proportional to the axial velocity, and the axial velocity component (VZ) 106 can be estimated.
The transverse oscillation (TO) blood velocity estimation approach has been used to estimate both VZ 106 and the transverse velocity component (VX) 108, along the transverse axis 110, of the velocity vector 112. With the transverse oscillation approach, a transverse oscillation is introduced in the ultrasound field, and this oscillation generates signals that depend on the transverse oscillation. The basic idea is to create a double-oscillating pulse-echo field using a one dimensional (1D) transducer array.
Color flow mapping (CFM) is one approach to visually show velocity. An example of this is shown in FIG. 2, in which first flow 202 through a first vessel 204 and second flow 206 through a second vessel 208 towards the transducer is displayed using a first color (red shades), and third flow 210 through the first vessel 204 and fourth flow 212 through the second vessel 208 away from the transducer is displayed using a second different color (blue shades). Intensity is proportional to the velocity of the flow.
Unfortunately, with color flow mapping, the two colors only show relative flow with respect to the ultrasound transducer. Furthermore, with color flow mapping, blood flow perpendicular to the ultrasound beam cannot be seen. Moreover, with color flow mapping, the colors do not indicate the direction and magnitude of the blood flow. In view of at least the above, there is an unresolved need for other approaches for visualizing blood flow.